The present invention relates to reducing aerodynamic drag on tractor-trailer rigs and in particular to reducing drag created by the interaction of cross-winds with a gap between the tractor and trailer.
Tractor-trailer rigs (or semi-trailers) are a vital element of product distribution. In the United Sates, tractor-trailer rigs travel over 100 billion miles a year consuming over 20 billion gallons of diesel fuel. It has been estimated that almost 65 percent of the fuel burned is to overcome aerodynamic drag. As a result, even a small reduction in aerodynamic drag may have a significant impact on the demand for diesel fuel reducing the cost of shipping products. Additionally, a reduction in demand results in a lower price for diesel fuel, further reducing costs of all diesel fuel consumers.
Many attempts have been made to reduce the aerodynamic drag of tractor-trailer rigs. Generally, these attempts are directed to drag created by the motion of the tractor-trailer rigs through the ambient air. For example, sloped tops, side extender fairings and side skirt bottoms have been added to the tractors. However, feasible side extender fairings and side skirt bottoms cannot reach rearward to the trailer because they would interfere with turning without complicated mechanical apparatus for retracting the skirts. Extended side fairings also block access to hoses and cables attached to the back of the tractor cab and to the front of the trailer, making safety inspections difficult, and also block access to access doors on the front of the trailer if so equipped.
Some fairings are attached to the tractor such as disclosed in U.S. Pat. No. 2,863,695, U.S. Pat. No. 3,241,876, U.S. Pat. No. 3,348,873, U.S. Pat. No. 4,458,937, U.S. Pat. No. 5,078,448, and others. Unfortunately these fairings are overly complex, expensive, and/or fail to address drag due to cross-winds.
For over 50 years it has been known cross-winds contribute to total drag. Other patents address the drag created by cross-winds, including U.S. Pat. No. 7,073,845, for “Aerodynamic Drag Reduction Apparatus for Gap-Divided Bluff Bodies Such as Tractor-Trailers” discloses flat vertical panels attached to the leading face of the trailer and overlapping with flat vertical panels attached to the trailing face of the tractor. While the fairings of the '845 patent address cross-winds, they require precise fitting to the individual tractor and trailer and may interfere with pneumatic hoses and electrical cables connecting the braking, lighting, and refrigeration systems on the tractor-trailer.
Another patent, U.S. Pat. No. 7,604,284 for “Vehicle Fairing Structure” discloses a fairing attached to the leading edges of the trailer to direct air away from the gap between the tractor and trailer. The fairing of the '284 patent is fixed to the trailer and not adjustable. It is not easily transferred between trailers and generally a separate fairing is required for each trailer, and it cannot be adjusted when the fifth wheel is moved forward or backwards based on weight distribution.
While known fairings provide some benefit, they are overly complex, expensive, and/or require custom fitting, and a need remains for a simple low cost fairing providing reductions in drag to reduce fuel consumption.